The present invention relates to a workpiece tensioning device for sewing and assembly units for pieces of cloth used in producing pants and the like. The sewing unit comprises a table with a work surface and a sewing machine having the well-known sewing and advancement elements is mounted on the work surface. The tensioning device includes movable gripping means provided with a jaw designed to grip one of the ends of the pieces of cloth. It also includes a control means connected to the gripping means and a return means adjustably mounted on the table that is connected to said gripping means. The return means is designed to keep the pieces of fabric or cloth taut as they are moved towards the sewing elements by the advancement elements and to return the gripping means to its starting position upon its release from the fabric. The devices which are used to keep the pieces of cloth to be assembled sufficiently taut, for example, the front and rear sections of the pants, are known and are considered essential although the sewing machines used in the aforementioned units are already regulated to ensure that the outer edges of the pieces of cloth are in alignment.
The difficulty in maintaining the edges of the pieces of cloth in alignment is mainly due to the fact that each section is differently shaped from the other.
In addition, the nature of the material which is used and the manner in which the sections are obtained makes a difference in length in the sections to be joined.
Generally, the two sections to be joined are matched by inserting the leading edges of both beneath the presserfoot of the machine and stretching the pieces slightly to adapt the shorter one to the longer and by applying a tensioning device to the trailing edge of the pieces which have been drawn out in this manner in order to maintain the desired tension until the sewing operation has been completed.
The known tensioning devices are disposed on special guide rails along which they are displaced to follow the sewing operation.
These guide rails are generally embedded in the work surface of the sewing unit on which the operation is taking place and they are inclined with respect to the direction of advancement of the cloth. It is necessary for the guide rails to be embedded in the work surface to keep the pieces of cloth stretched out and the inclination of the rails is designed to enable the tensioning device to follow the lateral displacements of the pieces of fabric with respect to the direction of advancement resulting from the varying profile of the edge to be sewn.
The above-mentioned embedding of the rails tends to reduce the width of the work surface and necessitates the provision of a plate extending the length of the rail to cover the gap which is formed between the work surface and the rail by virtue of the need to vary the direction of the rail as a function of the profile to be sewn.
The object of the present invention is to obviate the disadvantages resulting from the reduction of the work surface and the provision of the guide rail and the covering plate. The technical problem to be solved to attain this object consisted in providing a tensioning device capable of ensuring the necessary tensioning function without the use of rigid guides -- however orientable -- and of following all the displacements of the article to be assembled.